It is of importance when making decisions about getting the right coax for your Ham Station to understand that there are trade-offs that have to be considered between transmitter power, antenna gain, coax loss, erp, and your total Ham Station system performance.
Your bank account may also enter into the equation like most Hams.

The db differences in gains or losses on transmit and receive between the choices available to you are the important issue.

A difference of 3 db either way will not be apparent to the stations that you are communicating with on the other end; around the block or around the world. They won't hear or see (on the S meter) any difference if you run your transmitter at 50 watts instead of its maximum 100 watt output power as an example.
This is a difference of about 3db! The same ratio holds true comparing 500 watts with 1000 watts!
Now take this same analogy and apply it to coax.
Here is an example:
Your present coax is 100 feet long and has a loss of 3db per 100 feet.You change it to the same length, 100 feet, using a more expensive coax that has only about .1db loss per 100 feet.
(Very Expensive Stuff!)
This is about a 3db increase in signal strength to the antenna that you were loosing in the old coax.
The station on the other end usually won't know the difference, and usually, neither will your receiver!
A difference of 3 db or less between two antennas, two types of coax, or two station configurations is usually not sufficient to justify the higher costs of the more expensive, lower loss, coaxial cable unless you are a perfectionist with lots of money.

However, a difference of 6 db may well justify the more expensive approach with the higher quality coax or antenna setup.
Remember, if you can't increase your transmit or receive signal by at least 5 or 6 db or more, if may not be worth the effort and expense.

The tables below should help you decide what if any coax changes you need to make.
Color Key:Green shade 50 - 52 ohm

Coax dB Loss per 100 Feet using common coax types:

dB Loss / 100 feetFrequency Mhz
Cable Type

1.0

10

50

100

200

400

900

1000

3000

5000

6A, 212

.26

.83

1.9

2.7

4.1

5.9

6.5

9.8

23.0

32.0

8 MINI, 8X

1.1

2.5

3.8

5.4

7.9

8.8

13.0

26.0

LMR -240

.24

.76

1.7

2.4

3.4

4.9

7.5

7.9

14.2

18.7

8, 8A, 10A, 213 (RG8/8A hard to find )

.15

.55

1.3

1.9

2.7

4.1

7.5

8.0

16.0

27.0

9913, 9086, 9096

0.9

1.4

1.8

2.6

4.2

4.5

13.0

4XL8IIA, FLEXI 4XL

0.9

1.4

1.8

2.6

4.2

4.5

13.0

LMR-400

.9

1.2

2.5

4.1

4.3

LMR-500

.7

1.0

2.0

3.2

3.4

LMR-600

.6

.8

1.4

2.5

2.7

8214

.60

1.2

1.7

2.7

4.2

7.8

14.2

22.0

9095

1.0

1.8

2.6

3.8

6.0

7.5

9, 9A, 9B, 214

.21

.66

1.5

2.3

3.3

5.0

7.8

8.8

18.0

27.0

11,11A,12,12A,13,13A, 216

.19

.66

1.6

2.3

3.3

4.8

7.8

16.5

26.5

14, 14A, 217

.12

.41

1.0

1.4

2.0

3.1

5.5

12.4

19.0

17,17A,18,18A, 218, 219

.06

.24

.62

.95

1.5

2.4

4.4

9.5

15.3

55B, 223

.30

1.2

3.2

4.8

7.0

10.0

14.3

16.5

30.5

46.0

58

.33

1.2

3.1

4.6

6.9

10.5

14.5

17.5

37.5

60.0

58A, 58C

.44

1.4

3.3

4.9

7.4

12.0

20.0

24.0

54.0

83.0

59, 59B

.33

1.1

2.4

3.4

4.9

7.0

11.0

12.0

26.5

42.0

62, 62A, 71A, 71B

.25

.85

1.9

2.7

3.8

5.3

8.3

8.7

18.5

30.0

62B

.31

.90

2.0

2.9

4.2

6.2

11.0

24.0

38.0

141,141A, 400, 142, 142A

.30

.90

2.1

3.3

4.7

6.9

13.0

26.0

40.0

174

2.3

3.9

6.6

8.9

12.0

17.5

28.2

30.0

64.0

99.0

178B,196A

2.6

5.6

10.5

14.0

19.0

28.0

46.0

85.0

100

188A, 316

3.1

6.0

9.6

11.4

14.2

16.7

31.0

60.0

82.0

179B

3.0

5.3

8.5

10.0

12.5

16.0

24.0

44.0

64.0

393, 235

.6

1.4

2.1

3.1

4.5

7.5

14.0

21.0

402

1.2

2.7

3.9

5.5

8.0

13.0

26.0

26.0

405

22.0

LDF4-50A

.06

.21

.47

.68

.98

1.4

2.2

2.3

4.3

5.9

LDF5-50A

.03

.11

.25

.36

.53

.78

1.2

1.4

2.5

3.5

Note: These tables are typical specifications for comparison only.Values may not be exactly as quoted by a specific mfg.

Power Handling Characteristics of Coax

Power Handling Vs Mhz
Coax type

1.0

10

50

100

200

400

900

1000

55, 6A, 212

4000

1500

800

550

360

250

150

8 MINI, 8X

4000

1500

800

550

360

250

150

8, 8A,10A, 213

11000

3500

1500

975

685

450

230

9913, 9086, 9096

3500

1500

975

685

450

230

4XL8IIA, FLEXI 4XL

3500

1500

975

685

450

230

9095

11000

3500

1500

975

685

450

230

9, 9A, 9B, 214

9000

2700

1120

780

550

360

200

11,11A,12,12A,
13,13A, 216

8000

2500

1000

690

490

340

200

14,14A, 217

20000

6000

2400

1600

1000

680

380

17,17A,18,18A,
218, 219

50000

14000

5400

3600

2300

1400

780

55B, 223

5600

1700

700

480

320

215

120

58

3500

1000

450

300

200

135

80

58A, 58C

3200

1000

425

290

190

105

60

59, 59B

3900

1200

540

270

270

185

110

62, 62A, 71A, 71B

4500

1400

630

440

320

230

140

62B

3800

1350

600

410

285

195

110

141,141A, 400
142,142A

19000

9000

3500

2400

1600

1100

650

174

1000

350

160

80

80

60

35

178B,196A

1300

640

330

240

180

120

75

188A, 316

1500

770

480

400

325

275

150

179B

3000

1400

750

480

420

320

190

393, 235

25000

9500

6300

4300

2800

1700

402

9000

3500

2400

1600

1100

650

405

130

LDF4-50A

19000

6100

2600

1880

1310

906

563

551

LDF5-50A

44000

7700

7740

5380

3720

2550

1620

1520

LMR-400 Power handling = 2100 watts <30Mhz

Understanding the effects of ERP vs antenna gain.

ERP CHART

Antenna Gain (dbd)

100 Watts Input(Rounded)

1

126

2

158

3

199

4

251

5

316

6

398

7

501

8

631

9

794

10

1000

11

1259

12

1585

13

1995

14

2512

15

3162

16

3981

17

5112

18

6310

19

7943

20

10,000

Note that these numbers above assume no loss in feedline or antenna and used theCSG Calculator)You will always have some bit of loss in your feedline but this calculator is considering only power and antenna gain.

Example: Coax lossUsing 100 watts output from transmitter and assuming your old coax had 3db loss, with no changes to antenna system except replacing your old coax and also assuming the new coax has 0db loss, the ERP of the antenna system would increase by 3db and would be 199 watts.
This is a 3db gain achieved by the new coax.

Example: Antenna Gain

You use an antenna that has 6dbd gain vs the old one that had 0dbd gain.
What effect does this have on your erp?
By using the chart above, you will see that with 100 watts at the antenna feedpoint, your effective radiated power would be 398 watts!

Remember, you have to achieve about 6db gain or loss to to make much difference on the air to the other station on receive.

Using this table, you should see that with every 3db increase or decrease, your effectively doubling the ERP or cutting it in half.
Your feedline will always have some loss so in calculating your total antenna system loss, always subtract the total loss of your feedline from your antenna gain.

Example:

Your antenna gain is 6dbd.

Your coax loss is 2 db per 100 feet as stated by the mfg. You use 50 feet.

Velocity Factor of Propagation Through Coaxial CableThe velocity factor is the speed at which an RF signal travels through a material compared to the speed the same signal travels through a vacuum. The velocity of propagation is inversely proportional to the dielectric constant.
Lowering the constant increases the velocity.
Generally, the higher the velocity factor, the lower the loss through a coaxial cable.

"Typical" Velocity Factor of Coaxial Cable by type

VF%

Transmission line type

95

ladder line

82

twin-lead

79

coaxial cable / foam dielectric

75

RG-6 and RG-8 coax (thick)

66

RG-58 and RG-59 coax (thin)

General Rules for Coaxial CableD = diameter of insulation under the shield
d = diameter of inner conductor.

Velocity Factor, Velocity of Propagation, VpThe higher the velocity factor, the lower the loss through the cable.
Raising the D/d has no effect on Vp
Raising the dielectric constant lowers Vp